Rear Brake Pad worn into Wedge Shape (2010 hatchback)

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by Nor'easter, Dec 29, 2019.

  1. Nor'easter

    Nor'easter Junior Member

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    Had the rear wheels in the air today and noticed left rear had a draggy brake. 100K miles, likely brakes have never been serviced. I thought I'd investigate and perhaps lube the sliders. I pull the wheel, bust the caliper bolts loose, pull the caliper back and whoa....

    The outboard pad is nearly full thickness at the ID, worn nearly to metal at the OD. Wedge shaped. The piston is just about fully extended and the boot is twisted like a darned pretzel. Inboard pad looks normal. Rotor looks normal. The boot is stretched, probably will not gracefully return to proper place if I replace pads and push the piston back in. Sliders were fine.

    How on earth does this happen? Wrenching on cars since I was a kid in the 70s... this is a new one.

    Recommendations on OEM vs rebuilt calipers?

    I'm about to consult FSM on rear brakes... I have not worked on Prius brakes yet, these are a little different....

    edit: No spreader springs. This was probably a botched amateur job.
     
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  2. pingd

    pingd Member

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    Just curious: are the "spreader springs" the V-shaped clips on the top of the pads? (1:53 in this video)

    Good luck with this - wish I had some helpful advice but haven't done anything with the rear brakes yet (except lube the slide pins).
    This previous thread may interest you though:
    Seized rear left caliper | PriusChat
     
    #2 pingd, Dec 29, 2019
    Last edited: Dec 29, 2019
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  3. ChapmanF

    ChapmanF Senior Member

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    @Mendel Leisk will shortly be along and explain all. The twisted boot is a fabulous clue.
     
  4. Nor'easter

    Nor'easter Junior Member

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    I put the brakes back together just as they were (they aren't correct, but we can drive the car) until I figure out what my solution is going to be. Right now looks like a reman caliper and new pads.
     
  5. Mendel Leisk

    Mendel Leisk 'Orrible Oracle

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    LOL, you know it...


    @Nor'easter: Looking at the back of the pads (either one) is there a stubby protrusion:

    upload_2019-12-29_18-51-3.png

    Have you had the car since new; do you know it's brake service history (if any...)?

    Just wondering if these are aftermarket pads, and don't have the pin. That pin, when properly seated between the spokes on the caliper piston face, will prevent it turning, which otherwise will happen, with every application of the parking brake.

    Brake info in the attachment:
     

    Attached Files:

    #5 Mendel Leisk, Dec 29, 2019
    Last edited: Dec 29, 2019
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  6. Nor'easter

    Nor'easter Junior Member

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    Thanks Mendel, you even anticipated my next problem! I found the factory repair manual in pdf, but it has no index or table of contents. At something approaching 8000 pages...

    No service history on this car (price was right, just bought a couple months ago), but this has to be due to amateur work. It happens.
     
  7. ChapmanF

    ChapmanF Senior Member

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    Well, it's not quite fair to call that a problem of the factory repair manual. What you found was probably the big PDF that kicks around on the web, which was made by a bunch of different people* doing 'print to file' of section after section of the manual from the web, without showing the window titles (which in the real online version is where you see what everlovin' section it is that you're looking at), and glomming them all together into one PDF with no contents, links, or navigation.

    Text search is your only friend when trying to work with that sucker.

    No such problems when using the real manual online (more info).

    *you can tell because the online manual occasionally adds a page footer with the name of whoever was signed in to TIS and printed that page, and there are a bunch of different names in it, plus various whole sections came out with different margins, typefaces, etc.
     
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  8. Mendel Leisk

    Mendel Leisk 'Orrible Oracle

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    What are you viewing it with? Acrobat Reader or full Acrobat, if you click on the book mark tab, if it's the pdf I have, you'll see:

    upload_2019-12-30_9-51-33.png
    Click this:
    upload_2019-12-30_9-52-33.png
    Then choose "Collapse...", and you'll be seeing:
    upload_2019-12-30_9-53-32.png
    A little neater. Yes, there's still broken links, but the terminology they use stays very consistant, so if you need to find one of those, as @ChapmanF says just searching for a text string will usually work.

    If your pdf doesn't show bookmarks, pm me.

    Getting back to your brake problem, this may or may not be the same issue as yours, but have a read:

    I've had a beveled rear brake pad condition, but it was mainly the inside pad exhibiting bevelled wear, and I'm very familiar with the bozo who caused it. :oops:

    The first time I pulled off the rear caliper, I cleaned the pads/shims, lubed the caliper pins and paid no attention to the caliper piston orientation when reassembling.

    The caliper piston spokes (both sides) ended up riding up on aforementioned pins (intead of straddling them), creating a situation where all the pressure was bearing only that pin. Accordingly, my inboard side pads (the ones in contact with caliper piston) were severely worn at the ID, untouched at the OD. The inside face of the rotor was correspondingly about 50% rusty, from lack of pad contact.

    I discovered this about 6 months after the first brake job, noticing scoring on the outside face of rotor, and excessive drag. I opened things up and found the beveled pads. I ended up getting new pads, removed and scoured the rotors, relubed everything and reassembling, taking special care to get the piston orientation right, like this:

    upload_2019-12-30_10-8-42.png

    It's imperative to have the piston thus. Then, to ensure it stays that way, doesn't jump:

    1. Pump the brake pedal multiple times.
    2. Spin the wheel, verify it's spinning "relatively" freely. The rear disk brakes have a modest amount of drag, but with a good push of the wheel it should continue to free-spin two or three more revolutions.
    3. Lower car, reconnect 12 volt battery negative cable. (Good practice to disconnect for duration of brake work). Do not apply parking brake.
    4. Take the car for a short test drive, using the brakes gently.
    5. On return: apply/release the parking brake several times, raise the rear, verify wheels continue to spin semi-freely.

    In my case, after doing the above remedial steps, the brakes sounded terrible, basically because the new pads were running over rotors that had zones untouched for that 6 months. I really thought I should have change the rotors as well. I hung in there, and in a week or so the rotors were "healed", back to quiet.

    Wheel spin test:

     
    #8 Mendel Leisk, Dec 30, 2019
    Last edited: Dec 30, 2019
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  9. Nor'easter

    Nor'easter Junior Member

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    Happy New Year Mendel, you are one heck of a resource!
     
  10. Mendel Leisk

    Mendel Leisk 'Orrible Oracle

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    Best wishes to you in 2020 too. (y)
     
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  11. Nor'easter

    Nor'easter Junior Member

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    Did the brake job last night. Whoever was in here last was a real hack (now I have to go look at the fronts!).

    I wasn't as happy as I wanted to be with either caliper. I made 'em both work for the short run, but a pro wouldn't send them out the door.

    Reman calipers on order. At least the second time it goes faster. Grrrr.
     
  12. Eddie25

    Eddie25 Member

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    Out of curiosity, what do you mean by that exactly? Were the piston boots jacked or something?
     
  13. Nor'easter

    Nor'easter Junior Member

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    Neither piston was properly indexed for starters. On the left side, the outboard pad was cocked badly, the outside edge was worn to less than 2mm thickness, inside edge nearly full thickness -- this had to be an installation screw up. The inboard pad was little worn, the piston was well extended, boot twisted badly. Getting the piston to turn independently of the boot (required to press back in) required prying up the edge of the boot with an o-ring tool, lubricating with silicone brake grease. Unfortunately, the reason it was stuck was corrosion... and some of that corrosion is now inside the caliper seal... greatly increasing chance of leaks. Heck, it may be leaking already.

    On the right side, I had one badly seized slider and the one that wasn't seized completely had a torn boot. The manner in which it was torn was odd, inconsistent with anything I've ever seen happen in service, I'm inclined to think it happened when the last "mechanic" stuck his hands in here.

    Adventures in used cars....

    FWIW, unbeatable deal on reman calipers @ Amazon. I ordered about an hour ago and the price has dropped $2, lol. I've used Callahan calipers before on a Highlander, quality about as expected. Not OEM, but good enough.
     
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  14. Nor'easter

    Nor'easter Junior Member

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    I wouldn't ordinarily mention this, but the quality of the calipers I just received is so good I'd be sorta remiss otherwise. These calipers appear *new*. $104 for the pair, delivered, no core charge. I am very pleased.
     
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